High-Aspect-Ratio Microdevices and Methods for Transdermal Delivery and Sampling of Active Substances

ABSTRACT

High-aspect-ratio microdevices comprising microneedles, microknives and microblades and their manufacturing methods are disclosed. These devices can be used for the delivery of therapeutic agents across the skin or other tissue barriers to allow chemical and biological molecules getting into the circulation systems. The microneedles can also be used to withdraw body fluids for analysis of clinically relevant species when the device has an integrated body fluid sensor or sensor array in the vicinity of microneedles.

FIELD OF THE INVENTION

The present invention relates to high-aspect-ratio microdevices and themethod of making and using the same. The microdevices referred hereinclude microneedles, microneedle arrays, microblades, microbladearrays, microknives, and microknife arrays.

BACKGROUND OF THE INVENTION

Drugs are commonly administered in solid form through pills or capsulesthat can be orally taken. However, many biological drugs can not beadministered this way because of degradation in the gastrointestinaltract and quick elimination by the liver. Another common technique foradministration of drugs in liquid form is through injection using ametal hypodermic needle that can cause significant pain and discomfortto patients. A number of physical and chemical techniques includingelectroporation, laser ablation, ultrasound, thermal, iontophoresis andchemical enhancers have been explored to develop painless transdermaldrug delivery techniques. It was found that it's very difficult for themolecules with a molecular weight higher than 500 or diameter largerthan 1 nm to penetrate normal human skin. Further studies showed thatthe key barrier for transdermal delivery of substances is the stratumcorneum layer, the outer layer of skin, that is about 4-30 micron thick.Invasive methods to overcome this skin barrier have been used inpractice, such as intradermal (ID), intramuscular (IM) or subcutaneous(SC) injection using standard hyperdomic needles and syringes. Thesemethods cause pain and require a skilled professional. In addition, theymay cause needle injuries. Similarly, current method of extractingbiologic fluids such as blood from patients suffers from the samedisadvantages.

In order to improve the skin permeability of the therapeutic agents andother active ingredients, microneedles have been recently developed todisrupt the stratum corneum and facilitate the delivery of the activeagents and ingredients to the epidermis. These active substances canthen diffuse through the rest of epidermis to the dermis and absorbed byblood vessels and lymphatics there. The substance absorbed can get intocirculation system. Thus both topical and system-level delivery of drugsis possible. Since there are no nerves and blood vessels in stratumcorneum and epidermis, this is a minimally invasive, painless andblood-free method of drug delivery. An additional advantage of thismethod, when engineered for topical delivery of vaccines, can lead toenhanced inoculation effect because the epidermis is rich in antigenpresenting cells and is a desired target for vaccine delivery.

The prior art reports many devices and methods to overcome the skinbarriers. For example, U.S. Pat. No. 5,855,801 and U.S. Pat. No.5,928,207 assigned to The Regents of the University of California taughta microneedle fabrication method similar to IC compatible neuralrecording arrays. The disclosed microneedle arrays are typically lineararray as they are in the plane of the silicon substrate surface.Microneedles have been also fabricated by heating the glass tube andlengthening the heated part till the diameter of the tip is reduced tothe desired range. It's in general very difficult to control the size ofthe needle shaft and the tip this way although biologists are stillusing this method to produce microneedles that can inject or withdrawsubstances from a single cell.

U.S. Pat. No. 6,503,231 by Prausnitz et al discloses a method for makingout-of-the-plane porous or hollow microneedles. It either involvesporous silicon formed by anodization of silicon or deals withsacrificial molds or selective removal of substrate materials to formfluidic conduits. U.S. Pat. No. 6,511,463 by JDS Uniphase Corp. alsotaught a method to fabricate the same. U.S. Pat. No. 6,558,361 assignedto Nanopass Ltd. taught a method for the manufacture of hollowmicroneedle arrays by removing a selective area of substrate material.U.S. Pat. No. 6,603,987 assigned to Bayer Corp. also disclosed a methodto make hollow microneedle patch. All these methods are trying toperform certain functions of the current hyperdomic needles and create aminiaturized analog to perform drug delivery or extract body fluidswithout causing pain and discomfort.

More recently, U.S. 2004/0241965 discloses a method of making highaspect ratio electrode arrays comprised of solid metals. It involves thepreparation of porous microchannel glass template, electrodeposition ofmetals in the microchannels, and final preparation of electrode arrayfollowing electrodeposition. The body of microelectrode is formed byelectrodeposition method similar to those used in forming nanowires.

The prior methods to make microneedles, whether they are in-the-plane orout-of-the-plane from the substrate material, are cumbersome andexpensive. The hollow microneedle arrays, while their sizes are scaleddown from conventional needles, are especially expensive to make becauseof complexity in fabrication process. Their mechanical integrity alsosuffers as their sizes become smaller. Accordingly, a continuing needexists for an improved low cost, disposable transdermal delivery devicefor effective through skin delivery of substances in a controlledmanner.

SUMMARY OF THE INVENTION

The present invention provides methods for making high-aspect-ratiomicroneedles, microblades and microknives. Whether they are integratedwith microchannels and microreservoirs or not, these microdevices canserve as a platform for painless drug delivery or as sensors and sensorarrays for analysis of a patient's body fluids.

Little has been mentioned in the prior art on using solid microneedle toachieve efficient and efficacious transdermal delivery. It's unobviousthat solid microneedle, solid microblades and solid microknives can bepractically usable to deliver therapeutically meaningful dosage becausethere are no obvious fluidic conduits for fast transport or injection offluidics. It is unexpectedly found that the conduit opened up in thestratum corneum by piercing solid microneedles through skin can not becompletely closed even after the removal of microneedles. It istherefore the primary object of the present invention to provide atwo-step method for efficient and efficacious delivery of drugcompounds, vaccines and active cosmetic substances through skin. Thefirst step is the application of a microdevice comprising microneedles,or microblades, or microknives to the skin and open up hundreds orthousands of pathways in the stratum corneum layer. The length of needleor blade or knife is such that penetration depth does not reach dermislayer to cause any pain or discomfort. The second step is to immediatelyremove the microdvice and apply a skin patch that has active substancesembedded in it for controlled release of these substances. In thisregard, we disclose a safe, painless, and convenient method fortransdermal delivery of substrances such as drugs, vaccines and cosmeticcompounds.

Another objective of this invention is to disclose methods ofmicrodevices fabrication that can yield microdevices array with improvedmechanical strength using a combination of isotropic and anisotropicetch.

It is yet another object of the present invention to fabricatemicrodevices devices for controlled release of substances for anextended period.

Another object of the present invention is to fabricate high-aspectratio microneedles with increased needle length and sensors are placedin the vicinity of microneedle base, leading to a minimally-invasivediagnostic system. Sensor arrays are used to improve their selectivity.Compared to microneedles for drug delivery, microneedles with integratedsensors are larger to assure sufficient sampling of body fluids andtheir mechanical integrity can be assured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an embodiment of a microneedle arrayformed using the disclosed process flow illustrated in FIGS. 6A-6H.

FIG. 2 is a scanning electron microscope micrograph of a microneedlearray fabricated using the method disclosed in the Example 1 andillustrated in FIGS. 6A-6H.

FIG. 3 is a scanning electron microscope micrograph of microneedle arrayfabricated using the method disclosed in the Example 2

FIGS. 4A and 4B are perspective illustration and side cross-sectionalview of microknives.

FIGS. 5A and 5B are perspective illustration and side cross-sectionalview of microblades.

FIG. 6A to 6H are cross-sectional illustration of a fabrication processflow of a preferred method to form microdevices.

FIG. 7 shows level of cumulative amount permeated through skin forpureriran with and without microneedle treatment in an in vitro testusing the method disclosed in the current invention.

FIG. 8 shows plasma concentration of fluorescence-labeled bovine serumalbumin in rabbit tested in vivo at BSA loading in carbopol 934P of0.15%, 0.20%, 0.25%, 0.30% (Weight/Volume) for each microneedle arraythat has 400 microneedles. The total formulation amount is 1 mg onmicroneedle arrays.

FIG. 9 shows level of cumulative amount permeated through skin measuredin vitro for Botulinum Toxin Type A and Bovine Serum Albumin withmicroneedle treatment using the method disclosed in the currentinvention.

FIG. 10 shows interferon-alfa-1b activity measured in vivo on rabbitwith 4.8×10⁷ IU interferon-alpha-1b administered using method disclosedin the current invention as compared to subcutaneous injection of thesame amount of interferon-alfa-1b.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides high-aspect-ratio microstructures (HARMS)and methods of manufacturing the same, as well as their applications indelivery of drugs, vaccines, diagnostic agents and cosmetic substancesand sampling of body fluids.

Referring to FIG. 1, the preferred embodiment is a microdevice 9, havinga body 7 and a sharp tip 6 in the case of microneedles or sharp edge 6in the case of microblades and microknives. The body 7 and sharp tip 6,being out-of-plane on the substrate 1 are covered by a biocompatiblecoating 8 as illustrated in FIG. 6H. They may have embeddedmicrochannels, connecting to microreservoirs where the active substancesare stored.

Aspect-ratio is defined as the ratio of the depth or height of astructure to its lateral dimension. High-aspect-ratio microstructurestypically have an aspect ratio higher than about 5:1 and they may beuseful for a variety of purposes. In the current invention, the tip ofmicroneedle 6 or the edge of the microblade and microknife 6 needs to besharp in order to lower the insertion force, while the body ofmicrodevice 7 should be high enough to allow it to completely penetratestratum corneum. A typical size of the needle tip or width of edge onmicrobaldes and microknives is smaller than 10 microns, preferablysmaller than 5 microns and the height of the microdevices is higher than20 microns, preferably higher than 50 microns. The aspect ratio of thesemicrodevices, in a preferred embodiment of the current invention, arehigher than 10:1 with the size of the tip and edge smaller than 5microns and the height of microdevices higher than 50 microns. HARMS canthus be used to fabricate microdevices including microneedles,microblades, and microknives for drug delivery through skin or bodyfluids extraction out of skin. Another example of HARMS is microchannelsfor microfluidic manipulation and transport. HARMS is typically made byMicro-ElectroMechanical Systems (MEMS) or microfabrication technologythat involves a number of thin film deposition, photolithography,etching and electroplating, injection molding, hot embossing, as well asLIGA process.

Skin Strucutre

Skin has a biological barrier called stratum corneum in its outer layer.This layer of about 20 microns thick prevents most of the molecules frompenetrating through the skin. So far, the successful skin patch is onlyable to deliver drug molecules of less than 500 Da and these smallmolecules are typically limited to hydrophobic ones.

The layer below the stratum corneum is called viable epidermis.Epidermis is between 50 to 100 micron thick. The viable epidermis layerhas no blood vessels and the molecules in this layer can be transportedto and from the dermis, a layer under the viable epidermis, which isbetween 1 to 3 mm thick. There are blood vessels, lymphatics and nervesin dermis layer.

Requirement of Delivery of Drugs, Vaccines and Cosmetic Substances

Successful transdermal delivery of therapeutic drugs, vaccines andcosmetic substances needs a way to transport molecules, especially largemolecules through the skin barrier, stratum corneum. The substance canbe delivered into the skin in any form acceptable to pharmaceuticalrequirements, but a gel formulation is preferred to achieve controlledrelease of active ingredients.

The Microneedles

The microneedle devices disclosed herein can contain one or moremicroneedles. The length of the microneedle is typically in the range of20-500 microns, sufficient to pierce through the outer skin barrierlayer and deliver molecules to viable epidermis or even deeper. Thediameter of a single microneedle is typically in the range of 30-300microns with a sharp tip of less than 10 microns to cause little comfortto the patients while maintaining mechanical integrity. In oneemobodiment of the invention, the needle tip 6 is less than 2 micronsand the height of the needle shaft 7 is about 100 microns. The aspectratio is 50:1. Referring to FIG. 6H, the angle of the tip 10 is between30 to 75 degree, typically between 45-72 degree. FIG. 2 shows amicrograph of microneedle arrays fabricated by this method with a zoomin view of a single microneedle that has a base diameter of about 80microns. In another embodiment, FIG. 3 provides a micrograph of a“pyramid-like” microneedles with a base size of about 80 microns. Thesize of the microneedles is bigger for collection of body fluids andthey need to reach the dermis layer in the skin. In one emobodiment ofthe current invention, the inner diameter of needle tip is about 10microns and the height of needle is about 1200 microns to allowsufficient extraction of body fluids. The aspect ratio is 120:1.

The Microblades and Microknives

As shown in FIGS. 4 and 5, the microblades and microknives disclosedherein can contain one or more blades or knives. The sharp edge 6 ofthese devices is below 10 microns wide and the height of the body ismore than 100 microns. In a preferred embodiment of the currentinvention, the edge 6 is below 3 microns and the body height 7 is about150 microns. The skin contact area is about 0.003 mm×1 mm for eachmicroblade or microknife. The leading angle 10 of the blade edge isbetween 30 to 75 degree, preferably between 45-72 degree. It will becomeapparent from the following detailed description of the examples thatthe difference in manufacturing of microblade and microknife withrespect to microneedle is only the shape of the mask using across-sectional illustration of the fabrication process disclosed inFIG. 6A-6H.

Materials and Device Sterilization

The devices can be made of many different materials or theircombinations, including metals, ceramics, polymers and glass. Examplesof the materials are titanium, stainless steel, nickel, alloy ofnickel-iron, silicon, silicon oxide, glass, polymethyl methacrylate(PMMA), polyaryletherketone, nylon, PET, poly(lactic acid),poly(glycolic acid) (PGA), poly(lactic-co-glycolic acid) (PLGA),polycarbonate, and polystyrene. It should have enough mechanicalstrength to penetrate skin without break and buckle while ensuredelivery of drugs, or collect of biological fluids. They can besterilizable using established protocols (see, for example, moist heat,ethylene oxide or radiation sterilization as stated by ANSI/AAMI/ISO11134:1993, ANSI/AAMI/ISO 11135:1994 and ANSI/AAMI/ISO 11137:1994).

The Microchannels

High-aspect-ratio microchannels can be embedded in microdevices to allowflexible manipulation of microfluidics and connect microneedles to otherfunctional blocks such as drug reservoirs. Microchannels can be made ofmany different materials or their combinations, including metals,ceramics, polymers and glass.

The Microreservoirs

The microdevices can be connected to a reservoir with drug molecules andtheir proper formulations in liquid or solid forms. Microreservoir canbe made of many different materials or their combinations, includingmetals, ceramics, polymers and glass. In a preferred embodiment, themicroneedles are solid and the microreservoir is connected to the skinsurface through microchannels. The gel containing active component canbe dissolved by moisture evaporated from skin and the active substancecan diffusion into skin through conduits opened along the interface ofskin and microneedles. In another embodiment, the microneedles arehollow and they can be connected with drug reservoir through variousmicrochannels. The reservoir can be made of natural polymers, deformableelastic polymers, metals and ceramics as listed above.

Method of Use

The device described herein can be used to treat, prevent, or amelioratea body condition in need to treatment. The body condition can be amedical condition or a cosmetic condition. Representative medicalconditions include, but are not limited to, AIDS, breast cancer,melanoma, liver cancer, lung cancer, blood cancer, pituitary tumors,other cancers, flu, infection, blood disease, cardiac disease, backpain, neck pain, body pain, general pain, arthritis, osteoporosis,headache, depression, smoke, alcoholic, overweight and obesity,menopause, facial hair growth, balding, polycystic ovary syndrome, needof inoculation, need of anesthetics and in particular dermal disease.Representative cosmetic conditions include, but are not limited to, skinaging, skin wrinkle, dark spot, skin discoloration, moisturizing, skinlightening, skin whitening, skin firming, skin lifting, acne, wart,infection, irritation, dry skin and oily skin.

The microdevices of this invention are designed as disposable orre-usable devices. In one embodiment, the microdevices are disposable.Depending on whether the microdevices have coating of active substanceson them or not, there are three categories of applications in thedelivery of drugs, cosmetic substances and vaccines in the preferredembodiment.

For delivery of a drug, vaccine or cosmetic substance, in oneembodiment, the microdevices can be used to perforate or scratch stratumcorneum. They are then removed immediately and a skin patch with activesubstance is applied to the microdevice treated area right away. Theskin patch will stay on the skin for a pre-defined period, providingsustainable controlled release of active substances.

Another embodiment is to store the active agents, as defined below, inthe substrate and rely on passive diffusion when the microdevice is intouch with skin.

In yet a further embodiment, one can pre-coat microneedle shaft with aformulation that contains active substances. The coated microneedles areapplied to the skin and stay on the skin for the entire period oftreatment. The rate of through skin transport can be measured using invitro or in vivo methods known in the art.

Referring to FIGS. 7-10, the microdevices disclosed herein are effectivein increasing the through skin diffusion of molecules, especiallytherapeutic molecules with molecular weight higher than 500 Daltons andhydrophilic molecules to transport through skin barrier. As it will befurther explained in the Examples, the enhancement of transdermaltransport was also observed for small molecules with molecular weightlower than 500 Daltons as shown in FIG. 7, as well as large moleculeswith molecular weight higher than 500. Because of the height ofmicroneedles and microblades is limited, it will not reach thenerve-rich dermis layer and cause any discomfort to the subject.

Active Agent

Active agent or active substance that can be delivered usingmicrodevices are therapeutic agents. The term “therapeutic agent” isused here to refer to active agent that can treat, prevent, ameliorate abody condition or skin condition that needs treatment. A list ofexamples includes: drugs, vaccines, peptides, proteins, genes, DNAs,nutraceuticals and cosmetics. The drugs can be administered topicallyand at whole system level. Examples of the drugs as active agentsinclude, but not limited to antibiotics, hormones, steroids,anti-inflammatory drugs, protein drugs, DNA drugs whether natural orsynthesized, such as Recombinant Erythropoietin (rhEPO), Taxol®,Interferon-alpha-1b, Interferon beta, Interferon gamma, Emla®,Fluorouracil, Lidocaine, Salicylic acid, Pureriran, eflornithinehydrochloride, spironolactone, flutamide, insulin, nanoparticle drugs,Epidural, recombinant human parathyroid hormone, growth hormone,thyroid, cortisol, estrogen, progesterone, and testosterone. Examples ofvaccines active agents include, but not limited to: vaccine againstinfluenza (flu), diphtheria, tetanus, pertussis (DTaP), measles, mumps,rubella (MMR), hepatitis B, polio, haemophilus influenzae type b,chickenpox, tuberculosis, anthrax, yellow fever, rabies, AIDS, cancers,meningococcus, SARS and cholera. More examples of cosmetic substances asactive agents include, but not limited to: botulinum toxin type A,hyaluronic acid and its derivatives, acetyl hexapeptide-3, vitamin A,vitamin C, vitamin E, alpha-hydroxyacids, collagen and hormones.Diagnostic reagents are also included. Examples include, but not limitedto: quantum dots, functionalized nanoparticles, magnetic particles fordiagnostic purpose.

Drug Delivery

In one aspect, the present invention provides a device 10 for deliveryof therapeutic active agent as defined above across the skin barrier,stratum corneum layer. Once the substances pass the stratum corneum,there is less resistance for the substances to diffuse into thesubsequent layers of the skin: epidermis and dermis. The substances willbe absorbed by microvessels and lymphatics in the dermis layer anddelivered to entire human body. Microdevices disclosed in the currentinvention can enhance through skin penetration of molecules of molecularweight lower than 500 Dalton as shown in FIG. 7. Microdevices can alsoenable through skin transport of large molecules of molecular weighthigher than 500 Dalton as shown in FIGS. 8, 9 and 10. The molecularweight of Bovine Serum Albumin is 66,000 Dalton. The molecular weight ofBotulinum Toxin Type A is 150,000 Dalton and the molecular weight ofInterferon-Alpha-1b is 17,000 Dalton.

Topical Delivery of Cosmetic Substances

It's known to one in the art that certain substances have specificfunctions as cosmetics. For example, Botulinum Toxin Type A is a toxinthat blocks neuromuscular transmission when it is injected in smallamounts (e.g., 10 units per 0.1 ml injection volume) into specificmuscles to treat and reduce wrinkles on the face. The maximum dosagerecommended as a single injection for any one muscle at any spot is 25units. If overdosed or the injection is incorrectly performed, thepatient can be left with an immobile face or droopy eyelids till theeffect of the injection wears off. The side effects include numbness,swelling and headaches. Administered through microdevices disclosed inthe current invention, it's possible to provide a controlled release ofBotulinum Toxin Type A and keep an optimal local concentration toachieve the best result while minimize the side effects. In a preferredembodiment of this invention, gel patch with botulinum toxin type A isapplied to the skin pre-treated with microneedle array. A significantincrease in through skin penetration of botulinum toxin type A wasobserved as detailed in FIG. 9. No through skin transport was observedwithout application of microdevices. More examples were provided in theabove “active agents” section.

It's also evident that through skin transport on microdevices treatedskin has less dependency on molecular weight as observed in FIG. 9.Using the methods described herein, practically, any cosmetic substancescan be delivered using microdevices herein. Local concentration can beadjusted through loading and formulation for controlled release. In oneembodiment of this invention, one can deliver hyaluronic acid gelthrough diffusion enhanced by microdevices. Hyaluronic acid is asubstance that exists naturally in the body. A major important functionof hyaluronic acid is to carry and bind water molecules. Stabilizednon-animal hyaluronic acid does not contain animal protein and does notrequire a skin test prior to treatment. It's thus a preferred embodimentof this invention to use microdevices to delivery locally stabilizednon-animal hyaluronic acid to treat wrinkles and facial lines.

Yet, in a further embodiment of this invention, one can locally deliverycollagen by microneedles, e.g., for allergic skin test and controlledrelease of collagen into the skin.

Yet, another embodiment of this invention is to provide for localdelivery of acetyl hexapeptide-3. This molecule is a non-toxic,non-irritant compound that modulates the excessive stimulation of thefacial muscles, relaxing facial tension and it can reduce and preventthe formation of new wrinkles due to over-stimulation of facial muscles.More examples include but not limited to: vitamin A, vitamin C, vitaminE, alpha-hydroxyacids, and hormones.

Delivery of Vaccines

In a further aspect of the present invention, the method provided hereincan be used for topical delivery of vaccines below the stratum corneumlayer. The type of vaccines includes conventional vaccines as well asprotein, peptide, DNA vaccines and the like as previously described.

Controlled Release

The microdevices need to deliver drug molecules through skin at a ratethat is sufficient to maintain a therapeutic useful concentration inplasma. The size, density of the microdevices can be adjusted to meetthe delivery requirement. The microdevices can be further coated with aformulation that contains active therapeutic molecules, or vaccines, orcosmetic substances, together with polymer binders such as chitosan,carbopol 934P, cellulose and starch to form a dry film. Additionaladditives of rheology modifiers, surface active agents, stabilizer,rehydration agents may be used. The special formulation can control thedissolve rate of the active drug molecule and regulate the drug releaserate. One example for controlled release of bovine serum albumin isshown in FIG. 8. The microdevices may be integrated with embeddedmicrofluidic channels that connect to microreservoirs.

The Integrated Sensors

It is another aspect of the invention to provide a device in whichclinical biosensor and/or sensor arrays are fabricated in the closevicinity of these HARMS structures. For example, microneedle can collectan extremely low sample volume of body fluids from a patient and allowrapid point-of-care analysis of body fluids. In one embodiment, thesample volume extracted is below 0.1 microliter, typically around 0.01microliter.

Methods for HARMS Fabrication

The HARMS were fabricated using MEMS microfabrication technology. Thetypical fabrication process involved lithography, wet etch and dry etch,thin film deposition and growth, electroplating, as well as injectionmolding and hot embossing. One example of fabrication method was to useBosch process that allowed deep Si etch(www.oxfordplasma.de/process/sibo_(—)1.htm). It formed HARMS suitableeither as device body or mold for further processing. The aspect ratiowas higher than 5:1, independent to feature size and pattern shape aslong as the features can be defined by lithography. Another fabricationmethod was KOH or TMAH wet etch of single crystal Si substrate that is<100> orientation or <110> orientation. Yet another fabrication methodwas using HF solution to electrochemically form porous Si structures(www.techfak.unikiel.de/matwis/amat/poren/ps.html). Metals was used forthe fabrication of HARMS through a maskless process calledelectropolishing starting from a structure fabricated by traditionalmachining methods such as cutting, electro-discharge machining, milling,grinding, polishing and drilling (www.najet.com andwww.fischion.com/product_support/model_(—)110_application_notes.asp).Use of any single method herein or a combination of these methods asfurther disclosed in the examples below led to the form of desired HARMSdisclosed in the current invention.

EXAMPLE 1

Fabrication of Si Microneedles

Bosch etch process is a widely used MEMS process that is known in theart to etch deep vias and trenches. The current invention disclosed amethod that involved isotropic etch first to form microneedle tip 6 andsecond anisotropic Bosch etch later to form microneedle shaft 7 as shownin FIG. 6G.

Referring to FIG. 6A, a silicon wafer 1 of any crystal orientation withabout 1 micron of thermal oxide 2 coated on both sides was used assubstrate. Doping level in the silicon substrate was found to be notcritical. A chromium layer with thickness ranging between 0.2 to 20 nmwas sputtered onto the substrate. A layer of photoreist 3 was applied tofront side of the wafer as shown in FIG. 6B. It was patterned into anumber of circular islands with a diameter that was equal to the base ofthe microneedles as shown in FIG. 6C. The shape of the pattern waschanged to rectangular to form microknives and microblades. The Cr etchwas done using common method that have been known in the art. Cr filmserveed as hard mask to etch part of oxide and silicon substrate 4.Oxide 2 was patterned, as shown in FIG. 6D by either buffered oxide etchin solution or dry etch using CHF₃ or CF₄ as etching gases. In apreferred embodiment of the current invention, an isotropic etch of Siwas done using SF₆ only while the Cr and oxide mask materials were stillthere as shown in FIG. 6E. The undercut of Si substrate 1 formed the tip5 of the microneedles as shown in FIG. 6E. Once Si undercut reacheed thestage with about 20 microns left, Bosch process was used to performalternative deposition and etch cycles until the etch depth reached thepre-defined length of microneedles as shown in FIG. 6F. The final shapeof microneedles was formed by a short wet etch using a mixture of aceticacid, nitric acid and fluoric acid, known as HNA to the people in theart. HNA dip helped release the hard mask and sharpen the tip 6 of themicroneedle as shown in FIG. 6G. The formed microneedle was coated withabout 200-500 A Ti coating to improve biocompatibility as shown in FIG.6H. FIG. 2 shows a micrograph of microneedles fabricated in this way.

EXAMPLE 2

Fabrication of Si Microneedles

The current invention also disclosed a method that did anisotropic etchfirst to form microneedle body and switch to orientation dependent etch(ODE) later to form microneedle shaft and tip.

A silicon wafer of <100> orientation with 0.5-3 micron of thermal oxidecoated on both side was used as substrate as shown in FIG. 6A. The oxidewas patterned into a number of circular or square islands with adiameter that was roughly equal to the base of the microneedles. In oneexample, the diameter of the circular pattern was about 100 micron. Theoxide etch was done by either buffered oxide etch in solution or dryetch using CHF₃ or CF₄ as etching gases. Once silicon oxide etch wascompleted, Bosch process was used to perform alternative deposition andetch cycles until the etch depth reaches the pre-defined length ofmicroneedles, yielding a number of circular or square posts on thesilicon substrate. The final shape of microneedles, as shown in FIG. 6Gwas formed by KOH etch in a heated bath at a temperature between 20-90degree. The KOH concentration was between 10% to 80%. Typically, theetch temperature was between 50 to 80 degree and potassium hydroxide(KOH) concentration was between 20-50%. Tetramethyl ammonium hydroxide(TMAH) or sodium hydroxide was used to replace KOH to give similarresults. Typical etch condition was 20%-40% TMAH at about 80 degree.About 500 A Ti coating was applied to the formed microneedles to improvebiocompatibility as shown in FIG. 6H. FIG. 3 shows microneedle arrayfabricated in this way.

EXAMPLE 3

Fabrication of Microblades and Microknives

As shown in FIG. 6C, if the pattern is a rectangular shape, themicrodevices formed according to the process flow disclosed in theExamples 1 and 2 become microknives and microblades.

EXAMPLE 4

Fabrication of Polymer Microneedles

A stainless steel piece was used as cathode. A patterned conductivepiece with round posts on it was used as anode. The height of the postswas comparable to microneedle height. Both electrodes were immersed inan electrolyte and a voltage of 0.5-5 V was applied to them, a selectivearea of cathode was dissolved away, leaving behind arrays of cavity.Once the etch was complete, the stainless steel piece with microneedlebody in the shape of cavity was obtained. It was used as mold insert formicro-injection molding to obtain polymeric microneedles, usingmaterials listed previously.

EXAMPLE 5

Fabrication of Metal Microneedles

A metal piece such as stainless steel, or Ti or Ni was used as cathode.A conductive piece with a grid pattern on it was used as anode. The sizeof each square was comparable to base of microneedle. When bothelectrodes were immersed in an electrolyte and a voltage of 0.5-5 V wasapplied to them, a selective area of cathode were dissolved away,leaving behind arrays of microneddles. The tips 6 of the microneedleswere sharpened by electropolishing, yielding very sharp metalmicroneedle arrays.

EXAMPLE 6

Application of Microdevices

In one embodiment, Chitosan was purified before use as following: A 20 gof chitosan was dissolved in 1 L of 1% acetic acid solution. After itwas filtered under reduced pressure, 1 M NaOH was added into thefiltrate to produce precipitate. The precipitate was washed repeatedlywith de-ionized water until the pH value of rinse water was about 7. Theprecipitate was dried in a vacuum dry box under reduced pressure. Thepurified chitosan was milled to powder and was used in preparing stocksolution that may further contain additives of rheology modifiers,surface active agents, stabilizer, rehydration agents and a combinationof thereof to form a formulation. The known volume of chitosan stocksolution containing known amount of active agent was prepared bydissolving active agent in a chitosan stock solution. Skin patchcontaining active agent was prepared using the casting method incleanroom environment. The skin patch prepared this way was let dry atroom temperature.

The application of microdevice enabled skin patch was a simple two-stepprocedure. The first step was the perforation or scratch of skin using amicroneedles or microknives and microblades with a plastic handlerattached to them on the backside with no high aspect ratiomicrostructures. These microdevices were coated with a biocompatiblefilm and had no active agent on them. This step can also be replacedusing a spring-powered mechanical device with microneedle or microknivesor microblades loaded. For example, a lancing device with a disposablemicroneedle attached to the moving end. The second step was theapplication of skin patch prepared using a method disclosed herein tothe microdevice treated skin area. Spring-powered devices providedresults with better consistency.

In another embodiment, the microdevice arrays were coated with chitosanformulation and let dry in a dust-free atmosphere at room temperature.The microdevice containing active agent was applied to the skin manuallyor using a spring powered device. Adhesive tape was used to keep themicrodevice on the skin during the entire treatment cycle.

1. A microfabricated high-aspect ratio device for delivery of an activeagent, comprising a substrate formed of a material selected from thegroup consisting of metals, ceramics, silicon, glass, polymers, andcombinations thereof, wherein the structure is selected from the groupconsisting of microneedles, microblades, microknives, microchannels andmicroreservoirs and a combination thereof.
 2. The device of claim 1,wherein the metal is titanium, stainless steel, nickel, alloy ofnickel-iron, and wherein the polymer is selected from the groupconsisting of polymethyl methacrylate (PMMA), polyaryletherketone,nylon, PET, poly(lactic acid), poly(glycolic acid) (PGA),poly(lactic-co-glycolic acid) (PLGA), polycarbonate, polystyrene, and acombination thereof.
 3. A microfabricated device as defined in claim 1,additionally comprising at least one skin-contacting area that isconnected through microchannels to a reservoir with active agents.
 4. Amicrofabricated device as defined in claim 1, wherein themicrofabricated needles or knives or blades are coated with a thin dryreagent formulation that contains active agents for therapeuticapplications in treating, preventing, or ameliorating a body condition.5. A microfabricated device as defined in claim 1, wherein themicrofabricated micro-needle is within close vicinity of thebiosensor-array for body fluids analysis to determine a body condition.6. A method of making the microfabricated devices as defined in theclaim 1, comprising: performing a first isotropic etch to definemicroneedle tips or microknife edge, and performing a second anisotropicBosch etch to define microneedle shaft or microknife body.
 7. A methodof making microfabricated devices as defined in the claim 1, comprising:performing an anisotropic etch first to define the body of microneedleor microblade and performing orientation dependent etch of Si usingpotassium hydroxide or tetramethyl ammonium hydroxide or sodiumhydroxide solution.
 8. A method of making the microfabricated device asdefined in the claim 1, comprising moving one or two electrodes selectedfrom the group consisting of a working electrode with materials definedin the claim 2 which is the cathode and the counter electrode which is apatterned anode during electrochemical etch.
 9. A method of making themicrofabricated device as defined in the claim 1, comprising injectionmolding or hot embossing using polymer materials defined in the claim 2.10. A method of using the devices as defined in claim 1 for treating,preventing, or ameliorating a body condition, comprising pushing aplurality of microneedles through the outer layer of skin or scratchinga plurality of microblades or microknives on a preselected site of theskin, and followed by applying a skin patch containing active agentsover the preselected skin site.
 11. A method of using the devices asdefined in claim 4 for treating, preventing, or ameliorating a bodycondition, comprising pushing a plurality of microdevices through theouter layer of skin or scratching a plurality of microdevices at apreselected skin site.
 12. The method of claims 10 and 1 1, wherein theactive agent is a therapeutic agent selected from the group consistingof antibiotics, hormones, steroids, anti-inflammatory drugs, proteindrugs, DNA drugs, recombinant Erythropoietin (rhEPO), Taxol®,Interferon-alpha-1b, Interferon beta, Interferon gamma, Emla®,Fluorouracil, Lidocaine, Salicylic acid, Pureriran, eflornithinehydrochloride, spironolactone, flutamide, insulin, nanoparticle drugs,Epidural, recombinant human parathyroid hormone, growth hormone,thyroid, cortisol, estrogen, progesterone, and testosterone andcombinations thereof.
 13. The method of claims 10 and 1 1, wherein theactive agent is a cosmetic substance selected from the group consistingof botulinum toxin type A, hyaluronic acid and its derivatives, acetylhexapeptide-3, vitamin A, vitamin C, vitamin E, alpha-hydroxyacids,collagen and hormones.
 14. The method of claims 10 and 1 1, wherein theactive agent is selected from the group consisting of vaccines, proteinvaccines, peptide vaccines, gene vaccines and DNA vaccines, whethernatural or synthesized, against influenza (flu), diphtheria, tetanus,pertussis (DTaP), measles, mumps, rubella (MMR), hepatitis B, polio,haemophilus influenzae type b, chickenpox, tuberculosis, anthrax, yellowfever, rabies, AIDS, cancers, meningococcus, SARS and cholera.
 15. Themethod of claims 10 and 11, wherein the active agent is quantum dots,functionalized nanoparticles, magnetic particles or a combination ofthereof for diagnostic purpose.
 16. The method of claims 10 and 11,wherein the microdevice performs controlled release of active agentdefined in the claims 12, 13, 14 and
 15. 17. The method of claim 10,wherein the microdevice performs topical delivery of active agentdefined in the claims 12, 13, 14 and
 15. 18. The method of claims 10 and11, wherein body condition is a medical condition and/or cosmeticcondition.
 19. The method of claim 18, wherein the medical condition isone or plurality of AIDS, breast cancer, melanoma, liver cancer, lungcancer, blood cancer, pituitary tumors, other cancers, flu, infection,blood disease, cardiac disease, back pain, neck pain, body pain, generalpain, arthritis, osteoporosis, headache, depression, smoke, alcoholic,overweight and obesity, menopause, facial hair growth, balding,polycystic ovary syndrome, need of inoculation, need of anesthetics andin particular dermal disease.
 20. The method of claim 18, wherein thecosmetic condition is one or plurality of skin aging, skin wrinkle, darkspot, skin discoloration, moisturizing, skin lightening, skin whitening,skin firming, skin lifting, acne, wart, infection, irritation, dry skinand oily skin.